the guide for growing is 78f, thats what the say, how ever my plants seem to grow a lot quicker and i mean a lot quicker at 85f, sometimes its a high as 90, my plants show no signs of stress and they really are growing quicker then if the temp was below 80, however this depends on strains, where some of these plants grow naturaly the temp is in the 90s for most the day and sometimes its hotter, so 78f been a guide is not the temp that they naturally grow in, some do how ever so some plants will show signs of stretch like the edges of the leaves curling upwards etc, so id say see where your plants grow best and keep the temps in that range, i always kept the temp below 80f to make sure my plants where happy, but then i switched to hps and struggled to keep temps down but i then found i was wasting my time as my plants prefer the higher temps and grow quicker,